This invention relates to the formation of an external flare around the end of a metal tube. While the tube on which the flare is formed may be of various cross-sectional shapes, the invention is particularly concerned with flaring a tube of substantially elliptical cross-section. Such tubes are widely used as waveguides in microwave antenna feeder systems. When the elliptical tube is used as a waveguide, the end flare may, for example, abut a waveguide connector in order to establish electrical contact between the waveguide and the connector.
To establish good electrical contact between the waveguide and the connector, it is important that the metal end flare be soft and ductile, be free of cracks and be of substantially uniform thickness. Previously available flaring tools for forming elliptical flares have not been able to completely satisfy these criteria. The most widely used flaring tool repeatedly hits or works the metal at the end of the waveguide as the flare is being formed. As a result of such repeated working, the metal is work-hardened and becomes so brittle that the flare often cracks either during the flaring operation itself or when the waveguide connector is coupled to the waveguide. The previously available tool also thins the metal of the flare and forms a flare which may be thinner on the minor axis of the waveguide than on the major axis thereof. The non-uniformity in thickness, together with the hardness of the flare, makes it difficult to locate the flare in tight and full face-to-face contact with the waveguide connector and thus makes it difficult to establish a good electrical joint between the waveguide and the connector.